There were no previous generations of Pro iPhones. I get that these are replacing the XS and XS Max, but those were not designated Pro. When you put that label on, you have to give all of Pro devices storage to match.
Of course, it's going to be very obvious to most people that the new iPhone 11 is the direct successor to the XR, and the iPhone Pros are the direct successors to the X, XS, and XS Max.